Near infrared spectroscopy is recognized as an important diagnostic analytical tool in a wide variety of industries, including agriculture, medicine, and chemical and pharmaceutical production. The information obtained is used for checking source materials, process intermediates, and characterization and validation of finished products. The technique is based on measuring the wavelength dependent spectral response of materials (absorption, reflection, polarization etc.) as a function of wavelength. Each material has a unique spectral signature, which can be recorded and used for identification. These instruments may obtain spectral information utilizing either a broadband light source to illuminate a sample and a filter to select the wavelength reaching these detectors, or use dispersing elements (e.g. a grating or prism) or filters to select a single wavelength from a broad light source to illuminate the sample. The signal from the sample is then collected by a detector, which provides averaged information about a target area within the field of view of the instrument.
In cases where spatial information is required a typical solution is to perform multiple single-point measurements over different areas of the target, or scan the target. The resolution of the image is determined by the field of view of the detector. The main drawback of this technique is the length of time it takes to compile the multiple points that make up a spectral image, which limits the practicality of imaging instruments utilizing this approach.
It is also known to use detector arrays to obtain spectral data. In a typical prior art instrument broadband near infrared light source may be used to illuminate a target. The light from the target is passed through either a set of fixed wavelength transmission filters or a tunable filter that passes only a narrow spectral band. The light is then collected by an imaging detector array, which operates in the near infrared spectral range. The imaging array records the image of the target at a number of wavelengths and the collected data is used to construct a hyper-spectral cube consisting of the spectral responds of each point as a function of illumination wavelength. The performance of such prior art systems is limited by numerous factors:                The intensity of a wideband source within a spectral band is inversely proportional to the bandwidth, therefore in order to increase the signal intensity of a given source the spectral resolution must be sacrificed.        The use of discrete filters provides a limited data set consisting only of a small set of discrete wavelengths.        Tunable filters, such as a liquid crystal tunable filter, limit the field of view of the camera as well as the intensity of the collected signal.        The spectral range is limited by the material properties of the filters, e.g. liquid crystal tunable filters operate in the range of 1100–1800 nm, whereas significant spectral information is available at longer wavelengths.        
Selecting a wavelength from a broadband light source either by dispersive elements or filters results in low intensity that limits the types of measurements and samples that can be analyzed.
Tunable optical parametric oscillators produce narrow band light across a broad wavelength spectrum. They are very well known and have been available for many years. The OPO wavelength is determined by the choice of the non-linear crystal, the pump wavelength, the temperature of the crystal, and the orientation of the crystal with respect to the pump laser beam. Wide wavelength tuning is achieved by varying the angle between the optical axis of the crystal and the direction of the pump beam (angle tuning). The spectral resolution of the instrument is defined by the OPO linewidth. The linewidth of the OPO beam is primarily a function of the crystal material, the crystal orientation, and the pump wavelength, e.g. a relatively narrow linewidth of less than 10 cm−1 is obtained over a wavelength range of 410–2600 nm from an OPO incorporating a BBO crystal in a type II orientation, pumped at 355 nm.
Spectral imaging, and specifically NIR imaging, is well documented in the literature and in numerous patents: Prior art U.S. Pat. No. 5,528,368 presents a NIR imaging device (microscope) based on a broadband NIR light source and tunable filters. U.S. Pat. No. 5,679,954 discuses the use of special bundle of fiber optics to convey infrared light for infrared spectroscopy of solid compounds of organic base. U.S. Pat. No. 5,214,277 discloses a support structure for holding a sample (a pharmaceutical product) for NIR spectroscopy. U.S. Pat. No. 6,690,464 describes an instrument in which multiple LED emitting a various wavelengths are used as the light source. U.S. Pat. No. 6,323,944 discloses a system incorporating a white light source and two sets of filters for hyper-spectral imaging of fluorescence. U.S. Pat. No. 6,236,047 discloses a method for multi-spectral analysis of organic blood analytes in noninvasive infrared spectroscopy. The system includes a broadband source and filters. Applicants' Patents related to the present invention include U.S. Pat. Nos. 5,276,548 and 6,259,160 both relating to optical parametric oscillators. All of the above patents are incorporated herein by reference.